Which of the following is not a consequence of the Lanthanoid contraction?

Options

A. 5d series elements have a higher `IE_(1)` than 3d or 4d series
B. Zr and Hf have a comparable size
C. Zr and Hf occurs together in the earth crust in their minerals
D. High density of the sixth period elements

Answer

To solve the question "Which of the following is not a consequence of the Lanthanoid contraction?", we will analyze each option in relation to the concept of Lanthanoid contraction.

### Step-by-Step Solution:

1. **Understanding Lanthanoid Contraction**:
- The Lanthanoid contraction refers to the gradual decrease in the size of the lanthanide ions and atoms as we move from lanthanum (La) to lutetium (Lu). This occurs due to the poor shielding effect of the 4f electrons, which leads to a greater effective nuclear charge felt by the outer electrons.

2. **Analyzing the Options**:
- **Option 1**: "5d series elements have a higher ionization energy than the 3d or 4d series."
- This statement is true. The higher ionization energy of 5d elements compared to 3d and 4d is a consequence of the Lanthanoid contraction, as the effective nuclear charge increases due to the smaller size of the 5d elements.

- **Option 2**: "Zirconium and Hafnium have comparable size."
- This is also true. The comparable size of zirconium (Zr) and hafnium (Hf) is due to the Lanthanoid contraction, as the poor shielding by f-electrons results in similar atomic radii for these elements.

- **Option 3**: "Zirconium and Hafnium occur together in the earth's crust in their minerals."
- This statement is true as well. The similar size and properties of Zr and Hf lead to their occurrence together in minerals, which is a consequence of the Lanthanoid contraction.

- **Option 4**: "The high density of sixth period elements."
- This statement is true but is not a direct consequence of the Lanthanoid contraction. The high density of sixth period elements is influenced by other factors, such as the increasing atomic mass and the nature of the elements themselves, rather than the contraction of the lanthanides.

3. **Conclusion**:
- Based on the analysis, the option that is **not a consequence of the Lanthanoid contraction** is **Option 4**: "The high density of sixth period elements."

### Final Answer:
The answer is **4**: The high density of sixth period elements is not a consequence of the Lanthanoid contraction.

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